"John Edser"  wrote in message
news:cesh2d$avm$1{at}darwin.ediacara.org...
> JE:-
> Any relative fitness is a comparison.
> Any subtraction is just a comparison.
> What was being compared is what was being
> subtracted.

It is correct to say that a relative fitness is
a comparison - at least as most biologists use the
term "relative fitness".  It is a comparison between
two "absolute fitnesses".

However it is wrong to suggest that the comparison
is done by subtraction.  It is done by division.  At
least that is how it is done in population biology.

I did a Google on:
    "absolute fitness" "relative fitness"
I found many definitions of these terms.  There was
some variation in the definitions, particularly in
the definition of absolute fitness, but there was
near universal agreement that a relative fitness is
the ratio of two absolute fitnesses - not the difference.

Some examples:

http://www.uic.edu/classes/bios/bios101/Evolution/tsld037.htm
  Imagine there are several genotypes, each codes for a
  different phenotype. The genotype with the highest
  absolute fitness has a relative fitness of 1.0
  For every other genotype, their relative fitness is:
  absolute fitness of that genotype/absolute fitness
  of fittest genotype.

http://www.zoology.ubc.ca/~otto/PopGen500/Lecture1/Overheads.html
  Absolute Fitness : Average number of surviving offspring
  Relative Fitness : Fitness of one genotype divided by the
  fitness of a reference genotype.

http://www.bio.indiana.edu/courses/S318-brodie/S318/S318lect7.1-fitness.html
  RELATIVE FITNESS is useful in comparing individuals in a
  population, and it is absolute fitness divided by the average
  absolute fitness; the average relative fitness in a population
  is 1.

See also:
http://www.bio.indiana.edu/courses/S318-brodie/S318%20PPT/S318%20L%208%20fitness.pdf
http://www.holycross.edu/departments/biology/kprestwi/behavior/ESS/fitness.html
http://www.wsu.edu/~mmorgan/working/Elasticities/node8.html
http://www.uic.edu/classes/bios/bios101/Evolution/sld036.htm
   and the three slides that follow.
http://www.wordiq.com/definition/Fitness_(biology)

I didn't find a single reference suggesting that relative fitnesses
are calculated by doing a subtraction.

There was some variation in whether the reference (denominator) should
be the optimum or the average.  There was also some variation in what the
definition of absolute fitness should be, but a plurality used a
count of offspring.

And, there were some definitions that are just wierd - for example
the one in the Principia Cybernetica website.  But there were no
subtractions.

However, subtraction IS involved in calculating Hamilton's c.
"c" and "b" are differences between fitnesses.  The
difference can
be a difference between relative fitnesses or it can be a difference
between absolute fitnesses.  It doesn't really matter, as long as
you use the same kind of fitness difference for both "b" and "c".
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